OP
OP
Andrew_Culture
Internet Marketing bod
- Location
- The People's Republic Of Suffolk.
Carbon wheels, why would you bother?
- Thread starter Andrew_Culture
- Start date
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OP
OP
Andrew_Culture
Internet Marketing bod
- Location
- The People's Republic Of Suffolk.
Well I'm sticking with my Mavic open (rear) and MA3 rims laced to Ultegra hubs, and I'll just have to make sure I take a couple spoonfuls of Andrews Salts the night before a ride to reduce weight 
mattobrien
Guru
- Location
- Sunny Suffolk
I'll just have to make sure I take a couple spoonfuls of Andrews Salts the night before a ride to reduce weight
You have your own salts, wow. Depths, I never knew existed.
OP
OP
Andrew_Culture
Internet Marketing bod
- Location
- The People's Republic Of Suffolk.
Marginal gains
RecordAceFromNew
Swinging Member
- Location
- West London
Imho that biketechreview analysis is not particularly scientific - many conclusions seem to be based on the small difference between two much larger readings from a power meter, which accuracy is not great - some might say it is a common schoolboy mistake...
It is not too difficult to work out exactly the theoretical difference in power requirement of accelerating a wheel with the same mass concentrating at the rim vs one concentrated at the axle. The former has inertia, and the wheel would require exactly twice the power to accelerate compared to one with the mass concentrated at just the axle (and therefore has no inertia). The calculation is shown here. Conceptually we can visualise why it is so by appreciating rim mass at the bottom of the rim also has to be moved backwards when the wheel is moving forward, while the mass at the rim at the front of the wheel has to be moved downwards as well as forward etc. etc.
While it is true that a heavier wheel returns the energy when you decelerate, it is not much good to you if that energy happens to be the heat generated on your brake pads.
It is however indisputable that for most purposes the "speed performance" effect of wheel lightness alone is not great for most people. Nevertheless all else being equal if you have a choice you are better off having a light rim/tyre/tube than a light hub/frame/potbelly, and there are other reasons for having good, light wheels.
Dusty Bin
Guest
The science has already been done by Newton and others - all the article does is put generally accepted scientific principles into laymans terms in a cycling context. There is no need to re-invent the wheel....pun intended...
RecordAceFromNew
Swinging Member
- Location
- West London
I beg to differ. Deducing conclusions from the small difference of two much larger, somewhat inaccurate, numbers is not science.
Dusty Bin
Guest
I didn't say the article was 'science' - but the conclusions of the article are generally in-line with Newton's laws of motion. Which is the point I was making...
RecordAceFromNew
Swinging Member
- Location
- West London
It seems to me the article's conclusions are:
"So, what do all these numbers mean? It means that when evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant.".
The highlighted bit is the only bit that is true, according to Newtonian physics... and only under certain conditions that probably should have been qualified...
Dusty Bin
Guest
The bit about wheel inertia (ie rotating weight) is also consistent with established physics. It doesn't matter where the weight is on a wheel.
RecordAceFromNew
Swinging Member
- Location
- West London
My point is it does. A wheel that has mass concentrated at the rim requires double the power to spin up compared to one with the same mass all concentrated at the axle. The physics derivation is in the section entitled "Kinetic energy of a rotating wheel" in the Wikipedia article I linked to earlier. The biketechreview article's conclusion that wheel mass is of secondary importance and inertia of even less consequence is rubbish.
For those who are interested, such rubbish arose from experimental (rather than theoretical) "insight" arrived from noting the difference of power readings due to different wheel mass was c0.4% while c0.006% from different inertia, when he would be lucky to get within 1% accuracy from individual power meter readings, not to mention errors due to different environmental and other factors from different runs!
swee'pea99
Legendary Member
I'm no expert in wheels, much less Newtonian physics, but my personal experience is that changing from steel to 'proper' wheels, as I did on one of my bikes - which may have reduced my total rider + bike weight by something like half a kilo, ie, maybe 0.5% - made a helluva difference to the ride. Certainly the kinds of figures he's reporting:
...bear nothing like any relation to the subjective riding experience. And no, I wasn't 'fooling myself': riding with the '50% lighter' wheels was easier, quicker and livelier by an order of magnitude, not by .19%, 0.02%, or any other variant of bugger all you care to quote. And if Newton said otherwise, he's never ridden a bike.
...bear nothing like any relation to the subjective riding experience. And no, I wasn't 'fooling myself': riding with the '50% lighter' wheels was easier, quicker and livelier by an order of magnitude, not by .19%, 0.02%, or any other variant of bugger all you care to quote. And if Newton said otherwise, he's never ridden a bike.
Your bike weighed 100kg?
Even Zinn (whose calculations are referenced in that Wiki link you posted) thinks the rotational impact is almost negligible. It only really shows in heavy acceleration, and then it's small.
The conclusion in biketechreview and the Wiki article is the same: rim mass is less important than aero effect. Except perhaps on the steepest of climbs.
''Lighter bikes are easier to get up hills, but the cost of "rotating mass" is only an issue during a rapid acceleration, and it is small even then.''
So I am not really sure what your point is.
